Gas analyzing apparatus



J. D. MoRGAN Er A1. 204366 GAS ANALYZING APPARATUS Filed April 16, 1937 INENTORS Jo/f/v D. MORGAN ALAN 5 1 /VAN B/Ynuni( f l" f ATTORNEY Patented June 18, 1940 met PATIENT OFFICE GAS ANALYZING APPARATUS John D. Morgan, South Orange, N. J., and Alan P. Sullivan, Jackson Heights, N. Y., a'ssignors to Power Patents Company, Hillside, N. J., a

corporation of Maine Application April 16, 1937, Serial No. 137,167

2 Claims.

The present invention relates to gas analyzing apparatus, and is particularly concerned with apparatus for making quantitative measurements of the combustible components of gaseous mix- The invention is primarily concerned With measurement of combustibles in gaseous mixtures by the catalytic combustion of such gases within a combustion cell, with prior admixture therewith of a combustion supporting uuid. The invention herein described represents an improvement on the apparatus which is disclosed in our United States Patent No. 2,057,246 patented October 13, 1936.

The primary object of the present invention is to provide gas analyzing apparatus which is adapted for making accurate quantitative measurements of the combustible components both of gas mixture such as automotive exhaust gases which may contain up to 20% co-mbustible, as well as of mine gases or garage atmospheres contaminated with as little as .00.15 part of carbon monoxide and/or methane.

A more specic object is to provide a gas analyzer of the combustion type which is adapted for measuring both high and W concentrations of combustible in gas mixtures passed thereover, and the accuracy of which is not affected by substantial variations in the rate of flow of the gases over the catalyst.

With the above and other objects and features in view the invention consists in the improved gas analyzing apparatus which is hereinafter described and more particularly defined by the accompanying claims.

The invention will be hereinafter described more-particularly by reference to the accompanying drawing, in which- Figure 1 is a somewhat diagrammatic view of the gas circulating part of a preferred design of the apparatus; and

Fig. 2 is a wiring diagram embodying the catalyst heating elements of the analyzer shown in Fig. 1. Referring to the drawing, numeral Il (Fig. 2) designates an electric motor which is energized by current supplied thereto from a 6-volt D. C. circuit I2 controlled by a switch I4. Although not illustrated, the motor II) is operatively connected with two coacting positive pressure rotary blowers or pumps I6 and I8 (Fig. 1). The discharge port of pump I6 is communicably connected to the suction port of pump I8, as by a conduity 2U, and a valved relief pipe 22 is ported ut'o'f ,conduit 20 to atmosphere for the purpose of permitting free discharge fromthe pumping system of any excess volume of gas over that desired to be charged to the pump IS. The suction side of pump i6 is provided with a gas inlet pipe 2d which in turn communicates with the interior of a gas lter 25. The gas enters the filter i5 through a pipe 28. Another pipe Sil communicably connects with the suction side of pump lil for the purpose of supplying air from atmosphere to this pump. Pump I8 functions to continuously mixregulatedpro-portions of a gas which is to be analyzed for combustible and a combustion supporting gas, such as air, which mixture is discharged at a uniform regulated pressure from the pump discharge port through a conduit 32. y

The gas analyzer element consists of a housing li preferably comprising a block of Bakelite or other dielectric material, this housing beingpartitioned into separate.non-communicating combustion cells 35 and 58. The cell 38'is in perma nent communication with the atmosphere sur-l rounding the block 34 through a pipe 48, air lter 42, and radial apertures 44 in a dielectric plug ll which forms an end closure for the bottom of l cell 38. Filter 52 has an apertured removable base 48 and is lled with a loose packing of cotton, glass wool, or other dry filtering medium. The upper end of cell 3S is connected in permanent communication with the suction side oi pump I8 through a continuation of pipe 38 in the form of a channel 50 which is formed in the block 34. Air conduit is also connected with pipe 38 through a valved by-pass 52. This arrangement is such that by adjusting the valve in by-pass 52 a corresponding adjusment is made of the relative proportion of the incoming air which is drawn by pump I8 respectively through the cell 38 and through the by-pass 52. v

The upper end of analyzer cell 35 is ported to atmosphere through a passage 54. The lower end of cell 36 is in permanent communication with the discharge pipe 32 from pump I8 through a vertical extension 33 of pipe 32, and through radial apertures 5B which are formed in a plug 58 Awhich serves as the removable base closure for cell 36. A valved pressure relief conduit 66 is ported out of pipe 32 between the pump yI8 and. the combustion cell 36.

Within the cell 38, on a pair of parallel electric conductor supporting posts 52 extending upwardly into the cell from the removable plug v closure 46, there is mounted a pair of catalyst and non-catalyst wires 84 and 68 arranged in the form of a V with their lower ends connected at Uil the point G8 to form the apex of the V in approximately the vertical axis of the cell 38. Wires 64 and 66 form the active and inactive legs of a Wheatstone bridge electric circuit, the other two legs of which are designated in Fig. 2 by the numerals I and 12. Legs 64 and 66 are preferably constructed of approximately 1-1115" lengths of pure platinum wire having a diameter of about .001". The inactive leg 66 is preferably covered with a thin gold plating. It will be observed that both the catalyst and non-catalyst Wires 64, 66 are mounted in balanced relation within the cell 38 and are interconnected in the same Wheatstone bridge circuit. A ne coil spring I4 is arranged in the Wheatstone bridge circuit as one of the leads to a galvanometer 16. The coil spring I4 has another function, however, and that is to hold the wires 64 and 66 under uniform tension to prevent distortion thereof under the wide temperature changes to which the wires are subjected in use.

Mounted in the cell 36 on conductor supporting posts 'I8 is another pair of catalysts and noncatalyst wires S5 and 82, which are further illus trated in Fig. 2 as two of the legs of a second Wheatstone bridge circuit, the other legs of which are designated by the niunerals 84 and 86. The legs 8U and 82 of this second Wheatstone bridge circuit are preferably constructed of platinum alloy Wire. Because of the fact that the cell 36 is designed to measure quantitatively by combustion contents of combustible up to in gas mixtures pass therethrough, the catalyst leg 82 in the second Wheatstone bridge circuit is relatively insensitive in comparison to the catalyst leg 54 in cell 38. The catalyst leg 80 in cell 36 is preferably constructed of platinum-5% iridium alloy, and the non-catalyst leg 82 is preferably constructed of platinum-5% rhodium alloy plated with nickel oxide. Preferred dimensions for the legs 80 and 82 are wires 3/8" in length and .0035 diameter. Nickel oxide coating is used for wire 82 because the operating temperature of this wire is preferably in the neighborhood of 14001500 F. Wire 82 is constructed of a rhodium alloy of platinum, rather than an iridium alloy, because rhodium alloy is heated up to a higher temperature by a given unit of electric current passing therethrough, but this higher heating temperature is counteracted by the nickel plating which is used as most suitable for the high operating temperature, because a nickel plated catalyst seems to radiate more rapidly than does a clean platinum or platinum alloy wire at operating temperatures in the neighborhood of 1400- 1500 F.

As illustrated in Fig. 2, galvanometer 'I6 is provided with two scales, one of which is calibrated to give a full scale reading in the event that air containing as little as .15% of CO or other combustible contacts with the catalyst wire 84 in cell 38. The other scale of galvanometer 'I6 is calibrated to give a full scale reading when automobile engine exhaust gases, or other gas mixtures containing approximately 20% combustible, are passed over the catalyst 80 in cell 36. A double pole double throw switch 88 is provided for alternatively connecting the galvanometer lS either with the Wheatstone bridge circuit embodying catalyst wire 8U, or with the Wheatstone bridge circuit embodying catalyst wire 64. Because of the sensitive character of the catalyst 64 and its low maximum current carrying capacity, the Wheatstone bridge embodying this catalyst is provided with a shunt circuit 9U whereby current of approximately 1.10

amperes which is delivered by the supply circuit l2 to the Wheatstone bridge embodying the wires 80 and 82 in cell 36, is reduced to a current of approximately .42 ampere in the Wheatstone bridge circuit embodying the wires 64 and 66 in cell 38. A rheostat 92 is provided whereby to adjust the current supply to the Wheatstone bridge circuit from the main circuit I2, and additional rheostats 94 and 96 are provided for re spectively adjusting the zero settings and calibrations of the respective Wheatstone bridges embracing catalysts 64 and 80.

The operation of the apparatus will now be describedr briefly as adapted for use in making substantially simultaneous determinations of the combustible content of automotive engine exhaust gases and of atmospheric contamination at the point where the measurements are made. The end of a sampling pipe (not shown) is inserted into the exhaust pipe of the engine under test, and the switch I4 is closed, thus causing the motor Ill to function and supplying current to energize the two Wheatstone bridge circuits embodying catalysts 64 and 80. Under the action oi pump I6 the automotive exhaust gases are drawn from the sampling device into filter 26 and thence into the pump. The pump forces a measured portion oi' the gases through the pipe 2U into the suction side of' pump I8. Action of pump I B simultaneously serves to draw air thereto through the lter 42 and combustion cell 38. An inlet orifice 9B or" the filter is of such size that a substantial portion of the air drawn into the system uniformly passes through conduit 40 and radial apertures 44 into combustion cell 38 in contact with the heated catalyst wire 64, the temperature of which is normally in the neighborhood of 1200o F. Part of the air drawn into pump I8 may ow through by-pass connection 52. The air entering the pump I8 through pipe 3U is thoroughly mixed with the gas entering through pipe 20, and at a subsequent part of the pump rotor cycle this mixture of exhaust gases and air is expelled from the pump through conduit 32, and a measured portion thereof iiows continuously into combustion cell 36 through pipe extension 33 and radial apertures 56. After passing through the cell the gas makes its exit to atmosphere through the port 54. The valve in the relief pipe 60 is provided to release excess pressure built up by the pump I8 over that at which the analyzer has been calibrated to function.

The analyzer with its two combustion cells 38 and 36 forms a compact readily portable unit having a demountable set of base closures 46 and 58 respectively carrying the catalyst legs 64 and 80, so that any replacement of the delicate catalytic elements of the two Wheatstone bridge circuits can be easily made by an unskilled workman, as by simply substituting a new demountable unit comprising the plug closure 46, the wires 62, 64, 66, and 'I4 and the wiring which is integral therewith, in place of the unit removed.

By mounting the catalyst and non-catalyst legs of a bridge in the Same cell and in balanced relation, the ow of gas over these wires at a uniform rate is insured, thereby eliminating or minimizing variations in cooling effect of convection currents such as might occur in case the legs were mounted in separate cells. The elements l and 12 are preferably constructed of the same metal and with the same dimensions as ,the lopposite legs 64 and 66 in the Wheatstone bridge circuit which is operatively associated with the sensitive air analyzer cell 38. However, the

balancing legs 84 and 86 of the Wheatstone bridge circuit Which is operatively associated with cell 36 need not be constructed of the same material as the legs 80 and 82. These wires may advantageously be constructed of a base metal or'alloy such as manganin.

The invention having been thus described, what is claimed as new is:

1. In a gas analyzer, a combustion cell having mounted therein catalyst and non-catalyst legs of a Wheatstone bridge electric circuit, said legs comprising platinum alloy wires of substantially identical dimensions with a heat radiating nickel plating on the non-catalyst leg.

2. A gas analyzer unit comprising an air analyzer cell, a gas analyzer cell, a combined pump and mixing chamber, means for introducing to said pump at a uniform pressure and rate a stream of gas tov be analyzed, means for conducting a stream of air to be analyzed from atmosphere successively through the air analyzer cell and into the pump, means for conducting a mixture of air and gas at a controlled rate from the pump into the gas analyzer cell, catalyst Wires mounted in each cell adapted to promote combustion of combustible components in the air and gas streams respectively passing therethrough, and means for heating said catalyst wires electrically to temperatures at which combustion of combustible components will take place within the cells.

ALAN P. SULLIVAN.

JOHN D. MORGAN. 

